Broadband Airy Beam for Mid-Infrared Wave Enabled by Ge3Sb2Te6 Metasurface

As a novel phase change material, germanium antimony telluride (Ge3Sb2Te6) possesses the potential in the field of metasurface to dynamically manipulate wavefront and polarization of electromagnetic wave. In this work, Ge3Sb2Te6 meta-atoms are designed for the generation of Airy beam. Relying on the advantage of Ge3Sb2Te6 rod and gold substrate, tunable reflective phase and amplitude of meta-atom are realized through different rotation angles of Ge3Sb2Te6 rod. Due to the unique characteristics of Ge3Sb2Te6, meta-atom can flexibly change between half-wave plate and mirror reflector. As crystalline Ge3Sb2Te6 is adopted, cross-polarized wave is generated by meta-atom with a peak polarization conversion ratio (PCR) of 98% at 77.6 THz. On the contrary, as amorphous Ge3Sb2Te6 is employed, PCR is below 5%. Then, two exemplary metasurfaces are implemented as Airy beam generator and Airy beam focuser, and simulated results have a remarkable advantage of an overall bandwidth over 10 THz. The proposed metasurface may be applied in beam shaping and telecommunication.